Surface Water Infiltration in Loess Soils of the Lower Mississippi River Valley: An Emphasis on Land Use

The Alluvial Aquifer is the shallowest and most heavily used groundwater aquifer in the Lower Mississippi River Valley, particularly in the Delta region of eastern Arkansas. However, the Alluvial Aquifer is being depleted faster than the rate of recharge, primarily due to excessive withdrawals for irrigated crop production. Since extensive irrigation in the highly agriculturally productive Delta region of eastern Arkansas has been a main culprit in the groundwater depletion issues the region faces, a better understanding of how ecological factors and/or agricultural best management practices could possibly increase infiltration, to consequently increase recharge, are needed in order to either slow down or reverse the declining aquifer levels through the Delta region of eastern Arkansas. Therefore, the objective of this study was to evaluate the effects of landuse on surface water infiltration into alluvial and loessial soils in the Delta region of eastern Arkansas. Landuse combinations of interest included conventional and no-tillage agricultural practices, deciduous and coniferous forests, and native/natural grasslands. Replicate infiltration measurements were conducted using a double-ring infiltrometer, with a 15-cm inner-ring diameter, across multiple sites representing each of the five landuses. Despite the initial soil water content being greater (P \u3c 0.05) in the grassland than in all other ecosystems, the overall infiltration rate into the deciduous forest ecosystem (1.2 cm hr-1) was greater (P \u3c 0.05) than all other landuse types, which did not differ and averaged 0.10 cm hr-1. In addition, though the slope of the relationship between the natural logarithm of the infiltration rate versus the mid-point of time was unaffected (P \u3e 0.05) by landuse, the intercept parameter differed (P \u3c 0.05) among landuses. Results of this study demonstrated that landuse significantly affects infiltration processes in the fine-textured loessial and alluvial soils in the Delta region of eastern Arkansas; thus, further research is warranted into factors that can increase surface infiltration and potentially groundwater recharge

Constrained Evolution of a Radially Magnetized Protoplanetary Disk: Implications for Planetary Migration

We consider the inner $\sim$ AU of a protoplanetary disk (PPD), at a stage where angular momentum transport is driven by the mixing of a radial magnetic field into the disk from a T-Tauri wind. Because the radial profile of the imposed magnetic field is well constrained, a deterministic calculation of the disk mass flow becomes possible. The vertical disk profiles obtained in Paper I imply a stronger magnetization in the inner disk, faster accretion, and a secular depletion of the disk material. Inward transport of solids allows the disk to maintain a broad optical absorption layer even when the grain abundance becomes too small to suppress its ionization. Thus a PPD may show a strong middle-to-near infrared spectral excess even while its mass profile departs radically from the minimum-mass solar nebula. The disk surface density is buffered at $\sim 30$ g cm$^{-2}$: below this, X-rays trigger strong enough magnetorotational turbulence at the midplane to loft mm-cm sized particles high in the disk, followed by catastrophic fragmentation. A sharp density gradient bounds the inner depleted disk, and propagates outward to $\sim 1$-2 AU over a few Myr. Earth-mass planets migrate through the inner disk over a similar timescale, whereas the migration of Jupiters is limited by the supply of gas. Gas-mediated migration must stall outside 0.04 AU, where silicates are sublimated and the disk shifts to a much lower column. A transition disk emerges when the dust/gas ratio in the MRI-active layer falls below $X_d \sim 10^{-6}(a_d/\mu{\rm m})$, where $a_d$ is the grain size.Comment: 22 pp, 18 figures, Astrophysical Journal, in pres

Paying for health care in Vietnam: extending voluntary health insurance coverage

This discussion paper aims to synthesise a variety of reports and research projects conducted by the International Programme at the Centre for Health Economics, concerning the Vietnamese health system, over the past 4 years. In particular it focuses on the development of the state voluntary health insurance scheme which is the subject of a current DFID-funded research project. Previous work conducted by the members of the International Programme includes an investigation into the impact of economic reforms on the health system, an evaluation of the impact of user charges on access to health services amongst the poor, and a report providing an analysis of the state health insurance programme. The aim of the current research project is to analyse the experience of voluntary health insurance to date, making recommendations to policy-makers on its future development. A large household survey will form part of the investigations. The paper presents the situation to date, highlighting major developments, successes and failures, and the main challenges facing the scheme. The research project started in July 1998 and is due to be completed in March 2000.GDP, health insurance

Hot Electromagnetic Outflows II: Jet Breakout

We consider the interaction between radiation, matter and a magnetic field in a compact, relativistic jet. The entrained matter accelerates outward as the jet breaks out of a star or other confining medium. In some circumstances, such as gamma-ray bursts (GRBs), the magnetization of the jet is greatly reduced by an advected radiation field while the jet is optically thick to scattering. Where magnetic flux surfaces diverge rapidly, a strong outward Lorentz force develops and radiation and matter begin to decouple. The increase in magnetization is coupled to a rapid growth in Lorentz factor. We take two approaches to this problem. The first examines the flow outside the fast magnetosonic critical surface, and calculates the flow speed and the angular distribution of the radiation field over a range of scattering depths. The second considers the flow structure on both sides of the critical surface in the optically thin regime, using a relaxation method. In both approaches, we find how the terminal Lorentz factor, and radial profile of the outflow, depend on the radiation intensity and optical depth at breakout. The effect of bulk Compton scattering on the radiation spectrum is calculated by a Monte Carlo method, while neglecting the effects of internal dissipation. The peak of the scattered spectrum sits near the seed peak if radiation pressure dominates the acceleration, but is pushed to a higher frequency if the Lorentz force dominates, and especially if the seed photon cone is broadened by interaction with a slower component of the outflow.Comment: Submitted to the Astrophysical Journal; revised in response to the referee's comments [v1 incorrectly duplicated Figure 8a

The Algebra of Strand Splitting. II. A Presentation for the Braid Group on One Strand

Presentations are computed for a braided version BV of Thompson's group V and for V itself showing that there is an Artin group/Coxeter group relation between them. The presentation for V is obtained from that for BV by declaring all that all generators are involutions.Comment: 15 page

Between Boundaries: From Commoning and Guerrilla Gardening to Community Land Trust Development in Liverpool

Emerging in the cracks of the ownership model are alternatives to state/market provision of affordable housing and public/private‐led regeneration of declining urban neighbourhoods, centred on commoning and collective dweller control. This paper explores how the community land trust model can become an effective institutional solution to urban decline in the context of private property relations. It explores a case study of a CLT campaign in Granby, a particularly deprived inner‐city neighbourhood in Liverpool, England. The campaign seeks to collectively acquire empty homes under conditions of austerity, which have opened up the space for grassroots experimentation with guerrilla gardening, proving important for the campaign in gaining political trust and financial support. This paper discusses the potential of the CLT model as a vehicle for democratic stewardship of place and unpacks the contradictions threatening to undermine its political legitimacy